Day and Night Map
Quick answer: The amber curve on the map is the day/night terminator: the line where the sun is exactly on the horizon at this moment. Everything on the sunlit side is in daylight.
How to use day and night map
- Open the map in Live mode; the shaded side is night.
- Click a location or use Find to read its local sunrise, sunset and solar elevation.
- Choose a different date and time to compare seasons. Back to now resumes the 30-second refresh.
Worked example
- Input
- Around 06:00 UTC near the March equinox
- Expected result
- The overhead Sun is near 90°E; around 18:00 UTC it is near 90°W.
The subsolar point moves westward as Earth rotates eastward. The exact longitude also depends on the equation of time.
Calculation method and accuracy
The Sun’s declination sets subsolar latitude; right ascension and Greenwich sidereal time set its longitude. The terminator is the great circle 90° away from this point. The night fill follows the geometric horizon and is split into narrow longitude strips to avoid a seam across the date line.
Common mistakes and edge cases
- The map’s daylight boundary uses the geometric horizon, while sunrise times account for the conventional solar-disc and refraction threshold.
- Map projection exaggerates high-latitude areas. A half-dark map image is not required for half of the globe to be in darkness.
- Polar day and night are normal seasonal results, not missing map tiles.
Sources and verification
Reviewed by GeoDataViewer · . Examples are rounded; the interactive result uses your selected inputs.
Reading the terminator
The terminator is a great circle separating the sunlit half of the Earth from the dark half. It is not a line of longitude: it tilts through the year as the Earth's axis leans toward or away from the sun.
At the equinoxes the terminator runs almost exactly pole to pole. At the solstices it is tilted most, which is what leaves one pole in continuous daylight and the other in continuous darkness.
Twilight bands
Night does not begin the instant the sun sets. Civil twilight runs to 6° below the horizon and is when streetlights come on; nautical twilight to 12°, when the horizon is still visible at sea; and astronomical twilight to 18°, after which the sky is dark enough for serious observation.
In summer at high latitudes the sun may never get 18° below the horizon, which is why those places have no true astronomical night for weeks around the solstice.
Why the terminator is not vertical on the map
On a flat Mercator map the terminator appears as a curve, and its tilt changes with the season. That is a property of the projection, not of the terminator, which is always a circle on the globe.
Limitations to keep in mind
The terminator is drawn for a geometric sun position. Real twilight extends over a band rather than a line, and the atmosphere scatters light well into the night side, which this map does not attempt to shade.
Related tools
- Sunrise and sunsetSunrise, sunset and day length for any date and place.
- Sun positionWhere the sun is right now: elevation and azimuth.
- Moon phase calendarPhase and illumination for any date.
- Moon positionWhere the moon is overhead right now.
- Time zone mapCompare local times around the world.
Frequently asked questions
- What is the terminator?
- The line separating the illuminated half of the Earth from the dark half. It is where the sun is exactly on the horizon.
- Is this map live?
- It is calculated for the moment the page loads. Reload the page to refresh it.
- Why is the terminator curved?
- Because it is a circle on a sphere, and flattening a sphere onto a rectangle necessarily curves it.
- What are the three stages of twilight?
- Civil twilight ends at 6° below the horizon, nautical at 12°, and astronomical at 18°. Each stage is progressively darker.
- Why is there no night in summer in the Arctic?
- Because the Earth's tilt keeps the far north facing the sun continuously. The same tilt leaves the Antarctic in continuous darkness at the same time.
- What is the midnight sun?
- Continuous daylight for 24 hours or more, which happens inside the polar circles during the local summer.
- Does the map show twilight?
- The curve marks the day/night boundary itself. The twilight bands extend roughly 18° either side of it.
- Why does the day/night line move?
- The Earth rotates, sweeping the terminator westward at about 15° of longitude per hour, which is one full circuit per day.
- Is the day and night split always equal?
- Only at the equinoxes. The rest of the year one hemisphere receives more than twelve hours of daylight and the other less.
- Can I see the terminator from space?
- Yes, and it is one of the most striking features visible from orbit, appearing as a soft band of twilight rather than a hard line because of the atmosphere.